Boston’s homeless will have more places to escape the winter freeze, as Mayor Marty Walsh announced the opening of a homeless shelter at Southampton Street that will house about 490 people.

The closure in October of Boston’s largest homeless housing facilities on Long Island left hundreds of homeless to find shelter in city-owned facilities including the South End Fitness Center.

A dilapidated bridge that connects the island to the mainland was closed for repairs, cutting off access to the shelter and displacing hundreds of people just as the New England winter began to set in.

Advocates say the current situation is untenable, with some homeless people forced to sleep in parks and on city sidewalks.

Robyn Frost, the executive director of the Massachusetts Coalition for the Homeless, said Walsh’s plan to announce a new shelter for the city’s most vulnerable population as necessary and welcomed.

“It’s incredibly exciting to have more resources toward housing,” she said. “Pretty much anywhere in the city of Boston would work. The level of need will be quite substantial. If he kept on in this direction I would salute him greatly.”

Walsh’s said the 112 Southampton St. site is the current home of the Boston Transportation Department (BTD) sign should. It currently houses 48 workers and will be moved to a building at 12 Channel St. The plan is for BTD to move out by early January. Within a month, Walsh hopes the building will be able to accommodate 100 people. He hopes the shelter to be fully operational within three months. Walsh said his office is exploring ways to fund the project, including managing costs within the current budget, using current capital loan orders and supplemental budget funding.

“I’m happy to hear he’s looking for another place because he’s already struck out a couple times,” said Lynnel Cox, an addiction advocate and organizer who founded the group Hand Delivered Hope. “He’s reacting to what I consider to be a man-made emergency. There should’ve been a plan to deal with this beforehand.”

Cox said she hopes Walsh will also announce, “what he’s doing for recovery and addiction community.”

“I think housing for the homeless is great,” she said. “But homelessness causes addiction and addiction causes homelessness. We cannot forget about that. There’s a common denominator.”